Method of producing a magneto rotor

ABSTRACT

A plastoferrite pole ring is affixed to the inner circumferential surface of the casing bell of the rotor by an adhesive layer and pole pieces are similarly affixed to the inner circumferential surface of the pole ring in an assembly having an inner diameter somewhat smaller than the desired final value. A pressure plug is inserted, the outer surface of which has the desired final dimensions, and the assembly is heated, as the result of which the plastoferrite material is permanently deformed, retaining the desired exact dimensions after the removal of the plug. Projections may be provided on the casing bell and on the pole pieces to grasp into the plastoferrite ring.

United States Patent [191 [111 3,861,028

Mittag Jan. 21, 1975 [54] METHOD OF PRODUCING A MAGNETO 3,553,509 1/1971Schellekens 310/154 ROTOR 3,598,647 8/1971 Von Alten et a1. 29/596 ux3,728,786 4/1973 Lucas et al. 29/598 [75] Inventor: Hermann Mittag,Nuremberg,

Germany Primary Examiner-Carl E. Hall [73] Assignee: Robert Bosch GmbH,Stuttgart, Attorney, Agent, or Firm-Flynn & Frishauf Germany Oct. 1973[21] Appl- N05 407,970 A plastoferrite pole ring is affixed to the innercircumferential surface of the casing bell of the rotor by an [30]Foreign Application Priority Data adhesive layer and pole pieces aresimilarly affixed to Nov. H 1972 Germany 2255271 the innercircumferential surface of the pole ring in an assembly having an innerdiameter somewhat smaller 52 us. Cl 2 9 29 6 297 than the desired finalvalue- A Pressure P 1 156/312 3 ag 6 4 H 5 serted, the outer surface ofwhich has the desired final [51] Int. CL Hozk 15/04 dimensions, and theassembly is heated, as the result [58] Field 607 608 of which theplastoferrite material is permanently de- 29l523, l' l formed, retainingthe desired exact dimensions after 5 the removal of the plug.Projections may be provided on the casing bell and on the pole pieces tograsp into [56] References Cited the plastoferrlte ring.

UNITED STAT S PATENTS 4 Claims, 2 Drawing Figures 3,500,090 3/1970Baermann 310/154 METHOD OF PRODUCING A MAGNETO ROTOR This inventionrelates to a pole wheel for a magneto generator, particularly for aflywheel-mounted ignition system magneto of an internal combustionengine. Such a pole wheel, herein referred to as a magneto rotor, servesto rotate an array of permanent magnets around the outside of a fixedarmature structure.

It has been found advantageous to make such a magneto rotor out of apot-shaped magnetically conducting casi'ng bell provided with a hub formounting on an engine crankshaft or other drive shaft, carrying on itsinner circumferential surface an annular strip of synthetic materialcontaining embedded magnetizable particles and known as a pole ring. Thepole ring has magnetized zones which form pole faces at the innersurface of the pole ring, a pole piece of soft magnetic materialcommonly being applied on the inner surface of the pole ring to form thepole face surface. This type of pole ring is commonly referred to as aplastoferrite magnet or magnet structure.

It is known to manufacture a magneto rotor of the type above describedby riveting the pole pieces, pole ring and casing bell together,compressing the plastoferrite material between the pole pieces and thecasing of the pole wheel by the rivets and the like which pass throughthe plastoferrite material.

This form of construction has the disadvantage that the assembly of themagneto rotor requires several distinct operations that cannot easily becombined, because the mounting holes for the rivets must be provided,the rivets inserted and clinched and, finally, the pole face surfaces ofthe pole pieces must be machined to the design dimension of the innerdiameter of the rotor.

It is an object of this invention to provide an improved method ofmanufacturing a magneto rotor and to provide a form of rotor that can bemore easily manufactured. It is a further object to provide a form ofassembly of a magneto rotor comprising plastoferrite magnets that issubstantially simpler and more efficient and, in particular, to make itpossible to obtain the required inner dimensions of the pole faceswithout postassembly machining while still allowing the dimensions ofthe individual components to be subject to relatively wide tolerances.

Subject matter of the present invention: Briefly, an adhesive is appliedto the outer circumferential surface of the pole ring and/or to theinner circumferential surface of the pot-shaped casing bell, the polering is placed in position in the casing bell, at this time having aninner diameter somewhat less than the finally desired dimension, andthen a pressure plug is introduced inside the pole ring while theassembly is warmed to apply radial outward pressure against the innersurface of the pole faces, pressing the pole ring outwardly against theinner surface of the casing bell and producing a permanent deformationof the pole ring and pole surfaces to their desired final innerdimensions, after which the pressure plug is withdrawn.

In the case of magneto rotors in which the pole faces are provided bypole pieces, the manufacturing process of the present invention has thefurther feature that an adhesive is applied to the inner circumferentialsurface of the strip-like pole ring and/or the outer or the seatingsurface of the pole pieces and that the pole pieces are pressed by thepressure plug against the inner circumferential surfaces of themagnetized zones of the pole ring.

According to a further refinement of the invention projections areprovided on the inner surface of the casing hell that stick into thepole ring and the pole pieces have hook elements, such as bent edgesthat extend radially into the pole ring material for a short distance,so that all components of the structure are secured againstcircumferential relative displacement.

The invention will be described by way of example with reference to theaccompanying drawing. in which:

FIG. 1 is a cross-section of a magneto rotor of the present inventionwith the pressure plug used in its manufacture inserted therein, and

FIG. 2 is a front view of the same rotor with the pressure pluginserted.

FIGS. 1 and 2 show the pole wheel rotor 10 of a flywheel-driven ignitionmagneto generator. This rotor comprises a pot-shaped casing bell 11 madefrom a disc of sheet steel by a deep drawing process. On the innercircumferential surface of this casing bell 11 is a pole ring 12 in theform of a strip of rectangular crosssection, made of a syntheticmaterial containing embedded magnetizable particles, a so-calledplastoferrite material. The north and south poles of the pole ring areformed by magnetized zones 12a, the boundaries of which are shown bydashed lines in FIG. 2. On the inner circumferential surface of each ofthese magnetized zones a pole piece 13 is provided, the innercircumferential surface of each of which provides a pole face 13a. Thecasing bell I1 is also provided with a hub 14 for affixing it to acrankshaft of an internal combustion engine (not shown). To assemble themagneto rotor 10, a layer of adhesive 15 is applied to the outer surfaceof the pole ring 12 and/or to the inner circumferential surface of thepot-shaped casing bell 11. Likewise, an adhesive layer 17 is provided onthe inner circumferential surface of the pole ring 12 in the region ofthe magnetized zones 12a and/or on the outer or seating surfaces of thepole pieces 13. The pole ring 12 is then placed in position in thecasing bell 11 and the pole pieces 13 are applied to the innercircumferential surfaces of the magnetized zones 12a. At this stage theminimum inner diameter of the pole structure is somewhat less than thedesired final dimension. 7

A pressure plug 16 is then inserted into the pole wheel structure 10. Asshown in FIG. 2, this pressure plug engages the pole structure along thepole faces with radially extending regions 16a, the outer boundaries ofwhich have the design contour of the inner surface of the pole faces13a, hence supplying a circumference of somewhat larger diameter thanthe inner diameter of the pole face circumference prior to theintroduction of the pressure plug 16. That means that when the pressureplug 16 is inserted, the pole pieces 13 and with them also the pole ring12 of plastoferrite material are compressed outwardly against the innercircumferential surface of the casing bell 11, so that the pole ring 12and the pole pieces 13 are under pressure. The pole wheel rotor 10 alongwith the pressure plug 16 inside it are now heated. The adhesive layers15 and 17 then become fluid, so that unevenesses are smoothed out andthe opposed surfaces of the casing bell 11, the strip-like pole ring 12and the pole pieces 13 are stuck firmly together. At the same time thepole ring 12 is deformed, thereby relieving the pressure applied by thepressure plug 16. This is a permanent deformation, so

that after the cooling of the rotor that follows and the removal of thepressure plug 16, the rotor 10 has the proper intended value of innerdiameter at its pole faces without the necessity of a further machiningstep. The dimensional tolerances for the components such as the polepieces 13 and the pole ring 12 may be relatively large, becausedimensional variations to which these components may be subject arefully compensated by the deformation of the plastoferrite material ofthe pole ring 12 produced under the influence of heat.

Supplementary fastening means as well as further manufacturingoperations for fastening the pole pieces 13 and the pole ring 12 are notnecessary, because in a pole wheel rotor produced in accordance with thepresent invention thepole piecesv 13 adhere firmly to the inner surfaceof the pole ring strip 12 and the pole ring 12 likewise firmly adheresto the inner surface of the casing bell 11. The casing bell 11 and/orthe pole pieces 13, however, can be anchored in the plastoferritematerial of the pole ring 12 without any supplementaryassembly'operations if in the manufacture of the casing bell 11 a numberof projections 18, for example in the form of small claws, are providedon its inner circumferential surface and/or if in the manufacture of thepole pieces 13 radially outwardly extending, bent or peeled hooks 19 areprovided which will press into the plastoferrite material of the polering 12 when the pressure plug 16 is inserted into the structure andwill become firmly embedded therein.

Although the invention has been described with respect to a particularembodiment, it is not limited to that embodiment and modifications andvariations may be made within the inventive concept. For example, polewheel rotors can be made that have no pole pieces. In this case the polering itself has the pole faces 13a on its inner circumferential surfacein the region of the magnetized zones 12a. The pressure plug 16 must inthat case be so shaped that the entire inner circumferential surface ofthe pole ring 12 is compressed to the designed inner diameter dimension,instead of the pressure being applied only to the pole piece surfaces asshown in FIG. 2. As another example, the warming up of the rotorstructure 10 can take place before the insertion of the pressure plug 16or simultaneously therewith. The adhesive layers and 17 can, forexample, be made of an adhesive cement or by the application of a sheetof adhesive film.

Since a magneto rotor manufactured in this way can also have coarsetolerances for its outer diameter, the individual components of therotor can be manufactured and assembled largely without machining. Forprotection of the surface of the casing bell 11 and of the pole pieces13, they can be made of zinc plated sheet steel. If bare sheet steel isused, the completely assembled rotor 10 can be coated in a bonderizingbath.

1 claim: 1. A method of making a magneto rotor comprising a pot-shapedmagnetically conducting casing bell (11) with a hub (14) for mounting ona drive shaft and a pole ring (12) of synthetic material containingembedded magnetic particles on the inner circumference of said casingbell, which method comprises the steps of: applying an adhesive to atleast one of the matched circumferential surfaces respectively of saidcasing bell and of a pole ring of the aforesaid type having magnetizedregions and having an inner diameter slightly smaller than the desiredfinal dimension thereof; placing said pole ring in position in saidcasing bell on the inner circumfernetial surface thereof; introducinginside said pole ring a pressure plug (16) shaped to the desired finalinner dimensions of at least the magnetized regions of said pole ringand thereby exerting an outward radial force while, warming the assemblyand permanently deforming said pole ring to its desired final innerdimension; allowing the assembly to cool and said adhesive to harden andthereby to bind said matched surfaces, and thereafter withdrawing saidpressure plug. 2. A method as defined in claim 1 which also includes thestep of affixing pole pieces (13) to the inner circumferential surfaceof said pole ring (12), said pole pieces having surfaces matched to theshape of the inner surfaces of the magnetized regions of the said polering for mounting thereon, by applying an adhesive to at least one ofsaid matched surfaces respectively of said pole ring (12) and of saidpole pieces (13), and in which said pressure plug (16) is shaped to thedesired final spacing of inward facing pole face surfaces (l3a) of saidpole pieces as finally disposed with respect to each other, so that theintroduction of said pressure plug (16) inside said pole ring takesplace also inside said pole pieces and serves to exert outward radialforce against said pole pieces as well as indirectly against said polering, pressing said pole pieces (13) against the inner surface of themagnetized zones of said pole ring (12), after which said adhesive isallowed to harden to secure said pole pieces to said pole ring beforesaid pressure plug is removed.

3. A method as defined in claim 1 in which the adhesive (15) is warmedand becomes fluid when warmed and thereby binds the matched surfaces ofsaid casing bell (11) and said pole ring (12).

4. A method as defined in claim 2 in which an adhesive (15, 17) is usedwhich becomes fluid upon warming and is warmed and thereby binds thematched surfaces of said casing bell (l1) and said pole ring (12) and ofsaid pole pieces (13).

1. A method of making a magneto rotor comprising a pot-shapedmagnetically conducting casing bell (11) with a hub (14) for mounting ona drive shaft and a pole ring (12) of synthetic material containingembedded magnetic particles on the inner circumference of said casingbell, which method comprises the steps of: applying an adhesive to atleast one of the matched circumferential surfaces respectively of saidcasing bell and of a pole ring of the aforesaid type having magnetizedregions and having an inner diameter slightly smaller than the desiredfinal dimension thereof; placing said pole ring in position in saidcasing bell on the inner circumfernetial surface thereof; introducinginside said pole ring a pressure plug (16) shaped to the desired finalinner dimensions of at least the magnetizeD regions of said pole ringand thereby exerting an outward radial force while, warming the assemblyand permanently deforming said pole ring to its desired final innerdimension; allowing the assembly to cool and said adhesive to harden andthereby to bind said matched surfaces, and thereafter withdrawing saidpressure plug.
 2. A method as defined in claim 1 which also includes thestep of affixing pole pieces (13) to the inner circumferential surfaceof said pole ring (12), said pole pieces having surfaces matched to theshape of the inner surfaces of the magnetized regions of the said polering for mounting thereon, by applying an adhesive to at least one ofsaid matched surfaces respectively of said pole ring (12) and of saidpole pieces (13), and in which said pressure plug (16) is shaped to thedesired final spacing of inward facing pole face surfaces (13a) of saidpole pieces as finally disposed with respect to each other, so that theintroduction of said pressure plug (16) inside said pole ring takesplace also inside said pole pieces and serves to exert outward radialforce against said pole pieces as well as indirectly against said polering, pressing said pole pieces (13) against the inner surface of themagnetized zones of said pole ring (12), after which said adhesive isallowed to harden to secure said pole pieces to said pole ring beforesaid pressure plug is removed.
 3. A method as defined in claim 1 inwhich the adhesive (15) is warmed and becomes fluid when warmed andthereby binds the matched surfaces of said casing bell (11) and saidpole ring (12).
 4. A method as defined in claim 2 in which an adhesive(15, 17) is used which becomes fluid upon warming and is warmed andthereby binds the matched surfaces of said casing bell (11) and saidpole ring (12) and of said pole pieces (13).